Lens barrel

ABSTRACT

A lens barrel includes a cam ring which is rotated about an optical axis to move a lens group in the optical axis direction via a cam groove formed on the cam ring, and a rotational ring which transfers a rotational motion to the cam ring. The rotational ring includes a rotation-transmission arm extending in the optical axis direction. The cam ring includes an engaging recess formed on an outer peripheral surface of the cam ring, and in which the rotation-transmission arm is slidably inserted to be movable in the optical axis direction, and an outer flange formed on an outer peripheral surface of the cam ring to form a slot penetrating therethrough in the optical axis direction between the outer flange and a bottom radial surface of the engaging recess so that the rotation-transmission arm is slidably fitted in the engaging recess through the slot.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens barrel including a cam ring anda rotational ring. The cam ring moves along an optical axis directionwhile rotating about the optical axis by rotation of the cam ring.

2. Description of the Related Art

A type of lens barrel including a cam ring and a rotational ring whereinthe cam ring moves along an optical axis while rotating about theoptical axis by rotation of the cam ring is well-known in the art. Inthis type of lens barrel, the rotational ring is positioned around thecam ring. This arrangement has been a cause of increasing the diameterof the lens barrel. However, it cannot be said that miniaturization ofsuch a type of lens barrel has been extensively studied.

SUMMARY OF THE INVENTION

The present invention provides the aforementioned type of lens barrelwhich has structure making it possible to miniaturize the lens barrel,especially the diameter thereof.

For example, a lens barrel is provided, including a cam ring which isrotated about an optical axis to move at least one lens group in theoptical axis direction via at least one cam groove formed on the camring, and a rotational ring which transfers a rotational motion to thecam ring. The rotational ring can include at least onerotation-transmission arm extending in the optical axis direction. Thecam ring can include at least one engaging recess which is formed on anouter peripheral surface of the cam ring, and in which therotation-transmission arm is slidably inserted to be relatively movablein the optical axis direction, and an outer flange formed on an outerperipheral surface of the cam ring to form a slot which penetratestherethrough in the optical axis direction between the outer flange anda bottom radial surface of the engaging recess so that therotation-transmission arm is slidably inserted in the engaging recessthrough the slot.

It is desirable for the shape of the engaging recess to substantiallycorrespond to the rotation-transmission arm, and wherein a radial depthof the engaging recess is substantially the same as a radial thicknessof the rotation-transmission arm.

The cam ring is movable in the optical axis direction with respect tothe rotational ring, the rotation-transmission arm and the engagingrecess can be slidably engaged to be movable in the optical axisdirection.

It is desirable for the rotational ring to be prevented from moving inthe optical axis direction.

The lens barrel can further include a stationary barrel positionedaround the cam ring and include at least one cam-ring guiding cam grooveformed on an inner peripheral surface thereof, wherein the cam ring isrotated about the optical axis while moving in the optical axisdirection in accordance with a profile of the cam-ring guiding camgroove.

It is desirable for the rotational ring to be positioned in thestationary barrel so as to be rotatable about the optical axis withoutmoving in the optical axis direction with respect to the stationarybarrel.

The lens barrel can further including a movable ring positioned aroundthe cam ring, the movable ring being movable in the optical axisdirection, and a plurality of first bayonet prongs being formed on themovable ring. The outer flange can include a plurality of second bayonetprongs which are engaged with the plurality of first bayonet prongs sothat the cam ring and the movable ring move together in the optical axisdirection.

It is desirable for the lens barrel to further include another movablering positioned between the cam ring and the movable ring, wherein eachof the movable ring and the another movable ring is guided linearly inthe optical axis direction without rotating about the optical axis, andwherein the another movable ring projects forward from a front end ofthe movable ring when the lens barrel is in operation.

The lens barrel can include a motor which generates the rotationalmotion, so that the rotational ring transfers the rotational motion fromthe motor to the cam ring.

The lens group can include two movable lens groups, and the cam grooveformed on the cam ring can includes a plurality of first cam grooves,formed on an inner peripheral surface of the cam ring, for moving one ofthe two lens groups in the optical direction in a predetermined movingmanner, and a plurality of second cam grooves, formed on an outerperipheral surface of the cam ring, for moving the other of the two lensgroups in the optical direction in a predetermined moving manner.

The lens barrel can be a zoom lens barrel having a zoom lens opticalsystem including the lens group, a focal length of the zoom lens opticalsystem varying by rotation of the cam ring.

The rotation-transmission arm and the engaging recess can include aplurality of rotation-transmission arms and a corresponding plurality ofengaging recesses, respectively. The plurality of rotation-transmissionarms are engaged in the corresponding plurality of engaging recessesfrom the rear end of the cam ring in the optical axis direction,respectively.

In another embodiment, a lens barrel is provided, including a rotationalring driven to rotate about an optical axis by a motor, a cam ringrotated about an optical axis by receiving a rotational motion of therotational ring to move at least one lens group in the optical axisdirection via at least one cam groove formed on the cam ring. Therotational ring can include a plurality of rotation-transmission armsextending in the optical axis direction. The cam ring can include aplurality of engaging recesses which are formed on an outer peripheralsurface of the cam ring, and in which the plurality ofrotation-transmission arms are slidably inserted to be relativelymovable in the optical axis direction with respect to the plurality ofengaging recesses, respectively, and an outer flange formed on an outerperipheral surface of the cam ring to form a plurality of slots whichpenetrate therethrough in the optical axis direction between the outerflange and bottom radial surfaces of the plurality of engaging recessesso that the plurality of rotation-transmission arms are inserted in theplurality of engaging recesses through the plurality of slots,respectively.

In another embodiment, a lens barrel is provided including a cam ringwhich is rotated about an optical axis to move at least one lens groupin the optical axis direction via at least one cam groove formed on thecam ring, and a rotational ring which transfers a rotational motion tothe cam ring. The rotational ring can include at least onerotation-transmission arm extending in the optical axis direction. Thecam ring can includes at least one engaging recess which is formed on anouter peripheral surface of the cam ring, and in which therotation-transmission arm is slidably inserted to be relatively movablein the optical axis direction, and an outer flange formed on an outerperipheral surface of the cam ring to bridge the engaging recess in acircumferential direction, so that the rotation-transmission arm isslidably inserted in the engaging recess so as to be positioned insideof the outer flange in a radial direction.

It is desirable for the rotation transmission arm to also extend in acircumferential direction of the rotational ring, and for the slots andthe engaging recess to be also formed in the circumferential directionin accordance with the rotation transmission arm, the engaging recessextending in an area wherein the cam groove of the cam ring is notformed.

The present disclosure relates to subject matter contained in JapanesePatent Application No. 2001-335561 (filed on Oct. 31, 2001) which isexpressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below in detail with referenceto the accompanying drawings in which:

FIG. 1 is an exploded perspective view of an embodiment of a zoom lensbarrel according to the present invention;

FIG. 2 is an exploded perspective view of a portion of the zoom lensbarrel shown in FIG. 1;

FIG. 3 is an exploded perspective view of another portion of the zoomlens barrel shown in FIG. 1;

FIG. 4 is a perspective view of a second lens group moving frame and ashutter unit fixed to the second lens group moving frame, which areshown in FIG. 1, as viewed obliquely from front of the second lens groupmoving frame;

FIG. 5 is a perspective view of the second lens group moving frame andthe shutter unit fixed to the second lens group moving frame, which areshown in FIG. 1, as viewed obliquely from rear of the second lens groupmoving frame;

FIG. 6 is a view similar to that of FIG. 4, showing a position where thesecond lens group moving frame has rotated by a predetermined amount ofrotation with respect to the shutter unit from the position shown inFIG. 4;

FIG. 7 is a view similar to that of FIG. 5, showing a position where thesecond lens group moving frame has rotated by a predetermined amount ofrotation with respect to the shutter unit from the position shown inFIG. 5;

FIG. 8 is an axial cross sectional view of the zoom lens barrel shown inFIG. 1, above the optical axis, showing the zoom lens barrel in anaccommodation position;

FIG. 9 is a view similar to that of FIG. 8, showing the zoom lens barrelin a wide-angle position;

FIG. 10 is a view similar to that of FIG. 8, showing the zoom lensbarrel in a telephoto position;

FIG. 11A is an enlarged perspective view of the cam ring;

FIG. 11B is an enlarged perspective view of a rotational ring shown inFIG. 1;

FIG. 12 is a perspective view of the cam ring, the rotational ring and abiasing ring fitted on the rear end of the cam ring in the accommodationposition shown in FIG. 8;

FIG. 13 is a view similar to that of FIG. 12, showing the cam ring,rotational ring and the biasing ring in a photographing position;

FIG. 14 is a cross sectional view of the cam ring, the rotational ringand the biasing ring;

FIG. 15 is a perspective cross sectional view of the cam ring, therotational ring and the biasing ring;

FIG. 16 is a developed view of an outer peripheral surface of the camring;

FIG. 17A is a developed view of outer peripheral surfaces of the camring and the biasing ring fitted on the rear end of the cam ring;

FIG. 17B is a developed view of an outer peripheral surface of therotational ring;

FIG. 18 is a developed view of outer peripheral surfaces of the camring, the rotational ring and the biasing ring in the accommodationposition shown in FIG. 12;

FIG. 19 is a developed view of outer peripheral surfaces of the camring, the rotational ring and the biasing ring in the photographingposition shown in FIG. 13;

FIG. 20 is a developed view of an inner peripheral surface of the camring;

FIGS. 21A through 21J are developed perspective diagrams of the camring, a first lens group moving frame and the second lens group movingframe which are associated with one another, showing their positionalrelationships, step by step, in the case where the cam ring rotates fromthe accommodation position to the wide-angle extremity;

FIG. 22 is a graph showing variations in angle of rotation of the secondlens group moving frame with respect to the cam ring;

FIG. 23 is a graph showing the relationship among the angle of rotationof the cam ring and the axial positions of the first and second lensgroup moving frames, wherein their respective accommodation positionsare represented by the point of origin (zero) of the graph;

FIG. 24 is a perspective view of the first lens group moving frame andthe second lens group moving frame fitted in the first lens group movingframe in the accommodation position shown in FIG. 8;

FIG. 25 is a view similar to that of FIG. 24, showing a state wherethree linear guide keys of the second lens group moving frame andcorresponding three linear guide grooves of four linear guide grooves ofthe first lens group moving frame are aligned in the optical axisdirection of the zoom lens barrel so that the three linear guide keyscan be engaged in the corresponding three linear guide keys,respectively;

FIG. 26 is a front elevational view of the first lens group moving frameand the second lens group moving frame fitted in the first lens groupmoving frame in the accommodation position shown in FIG. 8;

FIG. 27 is a view similar to that of FIG. 26, showing a state where thethree linear guide keys of the second lens group moving frame and thecorresponding three linear guide grooves of the four linear guidegrooves of the first lens group moving frame are aligned in the opticalaxis direction of the zoom lens barrel so that the three linear guidekeys can be engaged in the corresponding three linear guide keys,respectively; and

FIG. 28 is a developed view of an inner peripheral surface of astationary barrel shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The illustrated embodiment of a zoom lens barrel, an explodedperspective view of which is shown in FIG. 1, is a telescoping zoom lensbarrel of a digital camera.

As can be clearly seen in FIGS. 8 through 10, the zoom lens barrel 10 isprovided with a photographing optical system constructed of three lensgroups: a first lens group L1, a second lens group L2, and a third lensgroup L3, in that order from the object side (the left side as viewed inFIGS. 8 through 10). The first and second lens groups L1 and L2 aredriven to move along an optical axis O relative to the third lens groupL3 while varying the distance therebetween to perform a zoomingoperation. The third lens group L3 serves as a focusing lens group, andis driven to move along the optical axis O to perform a focusingoperation.

As shown in FIG. 1, the zoom lens barrel 10 is provided with astationary barrel 11, a shaft holding member 12, a CCD holding frame 13,a low-pass filter 14, a rectangular sealing member 15, a CCD 16 and aCCD pressure plate 17, which are all stationary members fixed to acamera body (not shown). Namely, none of these elements either movealong an optical axis O (see FIGS. 8, 9 and 10) nor rotate about theoptical axis O. The stationary barrel 11 is fixed to the camera body byset screws. As shown in FIGS. 1 and 3, the stationary barrel 11 isprovided with an outer cylindrical portion 11 b and a gutter-shaped gearholding portion 11 c. Three cam grooves (cam-ring guiding cam groove) 11a are formed on an inner peripheral surface of the outer cylindricalportion 11 b at equi-angular intervals (intervals of 120 degrees) in acircumferential direction of the stationary barrel 11. The outercylindrical portion 11 b is further provided on the inner peripheralsurface thereof with three linear guide grooves lid extending parallelto the optical axis O. Three linear guide keys 27 a formed on a secondring (outer ring/movable ring) 27 are respectively engaged in the threelinear guide grooves 11 d. The zoom lens barrel 10 is provided with avertical motor 18 having a rotating shaft extending in a verticaldirection of the camera (the vertical direction as viewed in FIG. 1). Adrive gear 19 a of a reduction gear train 19 engaged with the rotatingshaft of the vertical motor 18 is mounted on the gear holding portion 11c to partly project into the inside of the stationary barrel 11 througha through hole (not shown) on an upper surface of the stationary barrel11.

The low-pass filter 14, the sealing member 15 and the CCD 16 are fixedto the rear face of the CCD holding frame 13 with the CCD pressure plate17.

The zoom lens barrel 10 is provided with a rotational ring 20 on which acircumferential gear portion 20 a meshing with the drive gear 19 a isformed. The rotational ring 20 is positioned in the rear of thestationary barrel 11 to be freely rotatable about the optical axis Owithout moving in the direction of the optical axis O (i.e., in theoptical axis direction) with respect to the stationary barrel 11. Threerotation-transmission arms 20 b project forwards from the rotationalring 20 at equi-angular intervals (intervals of 120 degrees) in acircumferential direction of the rotational ring 20. Each of the threerotation-transmission arms 20 b is provided on an inner surface thereofwith a rotation-transmission groove 20 c extending parallel to theoptical axis O.

The zoom lens barrel 10 is provided in the stationary barrel 11 with acam ring 22 positioned in front of the rotational ring 20. As shown inFIG. 11A, the cam ring 22 is provided, on an outer peripheral surfacethereof in the rear end of the cam ring 22, with three bottomed engagingrecesses 22 a shaped to substantially correspond to the threerotation-transmission arms 20 b. The rear end of each engaging recess 22a is formed as an open end. The radial depth of each engaging recess 22a is substantially the same as the radial thickness of eachrotation-transmission arm 20 b. The cam ring 22 is provided in thevicinity of the rear end thereof with an annular wall (outer flange) 23projecting radially outwards from the cam ring 22. The cam ring 22 isprovided on a front surface of the annular wall 23 with three bayonetprongs 24 each being elongated in a circumferential direction of the camring 22 and having an L-shaped cross section. The cam ring 22 isprovided, between an inner surface of the annular wall 23 and the threeengaging recesses 22 a and between the three bayonet prongs 24 and theset of engaging recesses 22 a, with three slots S (see FIG. 14)penetrating therethrough in the optical axis direction so that the threerotation-transmission arms 20 b are held between radial-bottom surfacesof the three engaging recesses 22 a and the respective inner surfaces ofthe annular wall 23 in the three slots S to be movable in the opticalaxis direction with respect to the cam ring 22, respectively. Each slotS has an arc shape which extends in a circumferential direction asviewed from the front (or rear) of the zoom lens barrel 10. The cam ring22 is provided in the three engaging recesses 22 a with three guide keys22 b which extend in the optical axis direction to be slidably engagedwith the three rotation-transmission grooves 20 c, respectively. The camring 22 is provided, on an outer peripheral surface thereof atequi-angular intervals (intervals of 120 degrees) in a circumferentialdirection of the cam ring 22, with three follower pins 22 f which extendradially outwards to be engaged in the three cam grooves 11 a of thestationary barrel 11, respectively. The front-end portion of the guidekey 22 b is positioned in the slot S.

The three rotation-transmission arms 20 b of the rotational ring 20 areslidably engaged in the three engaging recesses 22 a to be freelymovable in the optical axis direction with respect to the cam ring 22with the three guide keys 22 b being engaged in the threerotation-transmission grooves 20 c, respectively. The threerotation-transmission arms 20 b are respectively prevented from comingoff the three engaging recesses 22 a radially outwards by the annularwall 23, which is positioned radially outside the three engagingrecesses 22 a.

As shown in FIG. 3, the zoom lens barrel 10 is provided with a biasingring 21 which is fitted on the rear end of the cam ring 22 to bepositioned behind the annular wall 23. The biasing ring 21 is providedon an inner peripheral surface thereof with three recesses 21 a in whichthe three rotation-transmission arms 20 b are respectively inserted tobe freely slidable in the optical axis direction. The biasing ring 21 isprovided, on an outer peripheral surface thereof at equi-angularintervals (intervals of 120 degrees) in a circumferential direction ofthe biasing ring 21, with three recesses 21 b. The biasing ring 21 isfurther provided, on an outer peripheral surface thereof at equi-angularintervals (intervals of 120 degrees) in a circumferential direction ofthe biasing ring 21, with three follower pins 21 f in the close vicinityof the three recesses 21 b, respectively. The three follower pins 22 fof the cam ring 22 are engaged in the three recesses 21 b.

The biasing ring 21 is provided, on a front surface thereof atequi-angular intervals (intervals of 120 degrees) in a circumferentialdirection of the biasing ring 21, with three spring-support projections21 c, and the cam ring 22 is provided in the rear thereof with threespring-support recesses (not shown) formed to correspond to the threespring-support projections 21 c. One end of each of the threecompression helical springs 26 are inserted into the threespring-support recesses while the other ends thereof are fitted on thethree spring-support projections 21 c so that the three compressionhelical springs 26 are held under compression between the threespring-support recesses and the biasing ring 21. Accordingly, the camring 22 is always biased toward the front of the optical axis direction,while the biasing ring 21 is biased toward the rear of the optical axisdirection. Namely, the cam ring 22 and the biasing ring 21 are biased inopposite directions away from each other along the optical axis O by thethree compression helical springs 26.

As shown in FIG. 28, the three follower pins 21 f of the biasing ring 21and the three follower pins 22 f of the cam ring 22 are engaged in thethree cam grooves 11 a of the stationary barrel 11 at differentcircumferential positions, respectively. Each cam groove 11 a includes alinear groove portion 11 a 1, an accommodation groove portion 11 a 2, aposition-changing groove portion 11 a 3 and a zooming groove portion 11a 4. The linear groove portion 11 a 1 extends in the optical axisdirection. The accommodation groove portion 11 a 2 extends in acircumferential direction of the cam ring 22. The position-changinggroove portion 11 a 3 extends in a direction inclined with respect toboth the optical axis O and a circumferential direction of the cam ring22. The zooming groove portion 11 a 4 extends in a circumferentialdirection of the cam ring 22, i.e., extends parallel to theaccommodation groove portion 11 a 2. The three follower pins 21 f andthe three follower pins 22 f are inserted into the three cam grooves 11a via the linear groove portions 11 a 1 thereof, respectively.

In a state where the follower pins 21 f and the follower pins 22 f arerespectively engaged in the accommodation groove portions 11 a 2 (i.e.,in a state where the cam ring 22 is in an accommodationposition/fully-retracted position), a forward rotation of the motor 18causes the rotational ring 20 to rotate in a direction to extend thezoom lens barrel 10 relative to the stationary barrel 11. This causesthe rotational ring 20 to transfer the rotational motion thereof to thecam ring 22 due to the engagement of the three guide keys 22 b of thecam ring 22 in the three rotation-transmission grooves 20 c of therotational ring 20, respectively, so that the rotational ring 20, thebiasing ring 21 and the cam ring 22 rotate together about the opticalaxis O. Further forward rotation of the motor 18 causes each followerpin 21 f of the biasing ring 21 and each follower pin 22 f of the camring 22 to move from the accommodation groove portion 11 a 2 to theposition-changing groove portion 11 a 3, so that the cam ring 22 movesforward in the optical axis direction while rotating about the opticalaxis O. Further forward rotation of the motor 18 causes each followerpin 21 f and each follower pin 22 f to move from the position-changinggroove portion 11 a 3 to the zooming groove portion 11 a 4, so that thecam ring 22 rotates about the optical axis O without further moving inthe optical axis direction in accordance with the cam profile of thezooming groove portion 11 a 4.

As shown in FIG. 12, in a state where both the follower pins 21 f andthe follower pins 22 f are engaged in the accommodation groove portions11 a 2 (i.e., in a state where the cam ring 22 is in the accommodationposition), the three rotation-transmission arms 20 b are fully fitted(accommodated) in the three engaging recesses 22 a with the front endsurface of the circumferential gear portion 20 a of the rotational ring20 being in contact with the rear end surface of the biasing ring 21. Inthis state, the movement of the follower pins 21 f and the follower pins22 f to the zooming groove portion 11 a 4 via the position-changinggroove portion 11 a 3 causes the cam ring 22 and the biasing ring 21 tomove together forwards to enter a photographing position as shown inFIG. 13, with the rotational ring 20 remaining in the rear of thestationary barrel 11.

Thereafter, a reverse rotation of the motor 18 causes the follower pins21 f and the follower pins 22 f to move from the zooming groove portion11 a 4 toward the accommodation groove portions 11 a 2, performing amovement reverse to the above-described movement. At the same time, therotational ring 20, the biasing ring 21 and the cam ring 22 move fromthe photographing state shown in FIG. 13 to the accommodation positionshown in FIG. 12.

In the present embodiment of the zoom lens barrel, the rotational ring20, the biasing ring 21, the cam ring 22 and a barrier drive ring 44 arerotatable elements. The remaining movable elements, except for a secondlens group moving frame 31, linearly move in the optical axis directionwithout rotating about the optical axis O. The second lens group movingframe 31 can slightly rotate about the optical axis O. Such linearlymoving elements and linear guiding mechanisms thereof will behereinafter discussed.

As shown in FIG. 8, the zoom lens barrel 10 is provided between thestationary barrel 11 and the cam ring 22 with the second ring 27 and afirst ring (inner ring) 28 positioned in the second ring 27. The secondring 27, which is positioned just inside the stationary barrel 11, isprovided, on an inner peripheral surface thereof at the rear end of thesecond ring 27, with three bayonet prongs 27 c (only of which appears inFIG. 8) which are engaged with the three bayonet prongs 24 of the camring 22, respectively. Due to the engagement of the three bayonet prongs27 c with the three bayonet prongs 24, the second ring 27 is relativelyrotatable about the optical axis O with respect to the cam ring 22, anddoes not relatively move in the optical axis direction with respect tothe cam ring 22.

As shown in FIG. 1, the second ring 27 is provided, on an outerperipheral surface thereof at the rear end of the second ring 27, withthe three linear guide keys 27 a. The three linear guide keys 27 a areformed on the second ring 27 at equi-angular intervals (intervals of 120degrees) in a circumferential direction of the second ring 27 to berespectively engaged in the three linear guide grooves lid. The secondring 27 is guided linearly in the optical axis direction withoutrotating about the optical axis O with respect to the stationary barrel11 due to the engagement of the three linear guide keys 27 a with thethree linear guide grooves 11 d.

The second ring 27 is provided, on an inner peripheral surface thereofat equi-angular intervals (intervals of 120 degrees) in acircumferential direction of the second ring 27, with three linear guidegrooves 27 b which extend parallel to the optical axis O. The first ring28 is provided, on an outer peripheral surface thereof, at the rear endof the first ring 28 at equi-angular intervals (intervals of 120degrees) in a circumferential direction of the first ring 28, with threecylindrical projections 28 a which are engaged in the three linear guidegrooves 27 b, respectively. The first ring 28 is guided linearly in theoptical axis direction without rotating about the optical axis O withrespect to the second ring 27 due to the engagement of the three linearguide grooves 27 b with the three cylindrical projections 28 a. Each ofthe three cylindrical projections 28 a is provided with a radial hole 28a into which a follower pin 28 f (see FIGS. 8 through 10) ispress-fitted.

The first ring 28 is provided in the vicinity of the front end thereofwith an inner flange 28 b which extends radially inwards and to which abarrier unit 43 and the barrier drive ring 44 are fixed. The first ring28 is provided therein, on a rear surface of the inner flange 28 b, withthree guiding members 28 e (only one of them is indicated in FIGS. 1 and8) which extend in the optical axis direction. The zoom lens barrel 10is provided with a first lens group moving frame 29 which holds thefirst lens group L1 via a first lens group supporting frame 32. Thefirst lens group moving frame 29 is positioned in the first ring 28 tobe surrounded and supported by the three guiding members 28 e to beslidably guided thereby in the optical axis direction. Specifically, thefirst lens group moving frame 29 is provided, on an outer peripheralsurface thereof at the front end of the first lens group moving frame 29at equi-angular intervals in a circumferential direction of the firstlens group moving frame 29, with three linear guide grooves 29 a whichextend parallel to the optical axis O, and three linear guide keys 28 dwhich are formed on inner surfaces of the three guiding members 28 e toextend parallel to the optical axis O are slidably engaged in the threelinear guide grooves 29 a, respectively, so that the first lens groupmoving frame 29 is guided linearly in the optical axis direction withoutrotating about the optical axis O by the first ring 28.

The inner flange 28 b of the first ring 28 is provided on a rear facethereof, at equi-angular intervals (intervals of 120 degrees) in acircumferential direction of the first ring 28, with threespring-support protrusions 28 c (see FIGS. 8 through 10), and the firstlens group moving frame 29 is provided, on a front end surface thereofat positions thereon facing the set of spring support protrusions 28 c,with three spring-support recesses 29 b which are formed at equi-angularintervals in a circumferential direction of the first lens group movingframe 29. Three helical compression springs 30 serving as a biasingdevice are inserted to be held between the three spring-supportprojections 28 c and the three spring-support recesses 29 b,respectively, to press the first lens group moving frame 29 rearwards inthe optical axis direction. The first lens group moving frame 29 isprovided at the rear end thereof with three cutout portions 29 i inwhich three engaging projections 31 h formed on an outer peripheralsurface of the second lens group moving frame 31 at the rear end thereofare positioned, respectively (see FIG. 24).

The second lens group moving frame 31 that supports the second lensgroup L2 is fitted in the first lens group moving frame 29. The secondlens group moving frame 31 is provided, on an outer peripheral surfacethereof at the front end of the outer peripheral surface, with threelinear guide keys 31 a (see FIGS. 1 and 2) which are slidably engaged inthree linear guide grooves of four linear guide grooves 29 c (only oneof them appears in each of FIGS. 21A through 21J) which are formed on aninner peripheral surface of the first lens group moving frame 29 toextend parallel to the optical axis O. Due to the engagement of thethree linear guide keys 31 a with the three linear guide grooves 29 c,the second lens group moving frame 31 is guided linearly withoutrotating about the optical axis O by the first lens group moving frame29.

As can be understood from the above description, according to the abovedescribed linear guiding mechanisms, the second ring 27 is guidedlinearly in the optical axis direction without rotating about theoptical axis O via the stationary barrel 11, the first ring 28 is guidedlinearly in the optical axis direction without rotating about theoptical axis O via the second ring 27, the first lens group moving frame29 is guided linearly in the optical axis direction without rotatingabout the optical axis O via the first ring 28, and the second lensgroup moving frame 31 is guided linearly in the optical axis directionwithout rotating about the optical axis O via the first lens groupmoving frame 29, in that order from the outside to the inside of thezoom lens barrel 10.

The first lens group moving frame 29 is provided at the front endthereof with an inner flange 29 g which extends radially inwards to forma circular aperture having the center thereof about the optical axis O.As shown in FIG. 1, a female thread portion 29 d is formed on an innerperipheral face of the inner flange 29 g. A lens pressure ring 32 a isfixed to the rear end surface of the first lens group supporting frame32 that holds the first lens group L1. The first lens group supportingframe 32 is provided on an outer peripheral surface thereof with a malethread portion which is in mesh with the female thread portion 29 d ofthe inner flange 29 g. The first lens group supporting frame 32 iscemented to the first lens group moving frame 29 by adhesive after thethread engagement position of the male thread portion of the first lensgroup supporting frame 32 with respect to the female thread portion 29 dof the inner flange 29 g has been adjusted during assembly.

As shown in FIG. 2, the second lens group moving frame 31 is provided ona rear end wall thereof, at the center of the rear end wall, with acylindrical portion 31 b, the front and rear ends thereof being open. Anannular recess 31 c is formed between an outer circumferential wall ofthe second lens group moving frame 31 and the cylindrical portion 31 b.As shown in FIGS. 1 and 2, the second lens group L2 consists of twoseparate lens elements, a spacer ring 33 being positioned therebetween.The two lens elements of the second lens group L2 together with thespacer ring 33 are fitted in the cylindrical portion 31 b to be fixedtherein. As shown in FIGS. 5 and 7, the second lens group moving frame31 is provided on the rear end wall thereof with a first cutout portion31 d in the shape of an arc, and is provided, across the outercircumferential wall and the rear end wall of the second lens groupmoving frame 31, with a second cutout portion 31 e which is larger thanthe first cutout portion 31 d.

The zoom lens barrel 10 is provided in the annular recess 31 c of thesecond lens group moving frame 31 with a shutter unit 36. As shown inFIG. 2, a shutter support ring 35, positioned between the shutter unit36 and the second lens group moving frame 31, is provided on a frontsurface of a ring portion 35 a thereof with a support member 35 b whichprojects forward from the ring portion 35 a to support the shutter unit36. The shutter support ring 35 is provided on a rear surface of thering portion 35 a with a flexible printed wiring board (flexible PWB)fixing member 35 c which extends rearward from the ring portion 35 a.The shutter support ring 35 is provided at the center of the ringportion 35 a with a circular aperture 35 d in which the cylindricalportion 31 b is fitted. The shutter support ring 35 is loosely fitted inthe annular recess 31 c to be freely rotatable about the optical axis Owith respect to the second lens group moving frame 31 with thecylindrical portion 31 b being fitted in the circular aperture 35 d andwith the flexible PWB fixing member 35 c extending through the rear endwall of the second lens group moving frame 31 through the first cutoutportion 31 d. As shown in FIG. 2, the shutter support ring 35 isprovided on the support member 35 b with a linear guide key 35 eextending parallel to the optical axis O. The linear guide key 35 e isengaged in one of the four linear guide grooves 29 c, in which thelinear guide key 31 a which is not engaged, to be freely and slidablymovable therein in the optical axis direction. Accordingly, the shuttersupport ring 35 is not rotatable about the optical axis O since thefirst lens group moving frame 29 is not rotatable about the optical axisO either.

The shutter unit 36 is mounted on the support member 35 b, and is fixedto the support member 35 b by two set screws 35 f as shown in FIG. 2.

The second lens group moving frame 31 is provided, on the outercircumferential wall thereof in the vicinity of the front end of theouter circumferential wall, with three engaging holes 31 i positioned ona circle about the optical axis O. A shutter pressure plate 37positioned in front of the shutter unit 36 is provided, on an outerperipheral surface thereof, with three engaging projections 37 a whichare elastically engaged in the three engaging holes 31 i, respectively.The shutter support ring 35 and the shutter unit 36 are prevented fromcoming off the annular recess 31 c by the shutter pressure plate 37 in amanner such that the shutter pressure plate 37 closes the front end ofthe annular recess 31 c with the three engaging projections 37 a beingengaged in the three engaging holes 31 i (see FIGS. 4 and 6).

The shutter pressure plate 37 is provided on a front surface thereofwith three engaging protrusions 37 b. A low-frictional ring sheet 38 isfixed to a front annular surface of the shutter pressure plate 37 to beheld between the three engaging protrusions 37 b and the front annularsurface of the shutter pressure plate 37. The low-frictional ring sheet38 is made of a low-frictional material such as a tetrafluoroethyleneresin.

The shutter unit 36 is provided with shutter blades 36 a (see FIGS. 8through 10). The shutter unit 36 drives the shutter blades 36 a to openand close in accordance with information on an object brightness. Thezoom lens barrel 10 is provided therein with a flexible printed wiringboard (flexible PWB) F, one end (front end) of which is fixed to theshutter unit 36 (see FIGS. 8 through 10). A drive signal is given to theshutter unit 36 via the flexible PWB F. As shown in FIGS. 8 through 10,the flexible PWB F extends rearward from the shutter unit 36 on an uppersurface of the flexible PWB fixing member 35 c therealong, and bendsradially inwards to subsequently extend forward. Subsequently, theflexible PWB F is fixed to a lower surface of the flexible PWB fixingmember 35 c with adhesive tape, and bends radially inwards to extendrearward. Subsequently, the flexible PWB F extends through the CCDholding frame 13 via a through-slot 13 a (see FIG. 1) formed thereon,and bends radially outwards to extend upwards along a rear surface ofthe CCD holding frame 13. Subsequently, flexible PWB F bends to extendforward and above the stationary barrel 11. The second lens group movingframe 31 is provided on a rear surface thereof with a flexible PWBsupport member 31 j (see FIG. 8) for supporting (taking up) the slack ofthe flexible PWB.

The zoom lens barrel 10 is provided with a third lens frame 39 to whichthe third lens group L3 is fixed. As shown in FIG. 1, the third lensframe 39 is guided in the optical axis direction via a pair of linearguide rods 40 which extend parallel to the optical axis O. The front andrear ends of each linear guide rod 40 are fixed to the shaft holdingmember 12 and the CCD holding frame 13, respectively. The third lensframe 39 is driven to move in the optical axis direction by rotation ofa feed screw shaft 41 which is driven forward and backward by a stepmotor (not shown) in accordance with information on a photographingdistance.

A zooming operation is carried out by moving the first and second lensgroups L1 and L2 (the first and second lens group moving frames 29 and31) in the optical axis direction relative to the third lens group L3while varying the distance therebetween. The cam ring 22 is provided, onan inner peripheral surface thereof at equi-intervals (intervals of 120degrees) in a circumferential direction of the cam ring 22, with threelens-drive cam grooves (first cam grooves) C1. The first lens groupmoving frame 29 and the second lens group moving frame 31, which areguided linearly in the optical axis direction without rotating about theoptical axis O, move in the optical axis direction by rotation of thecam ring 22 in accordance with the profiles of the lens-drive camgrooves C1. FIG. 20 shows a developed view of the lens-drive cam groovesC1. The zoom lens barrel 10 is characterized in that each lens-drive camgroove C1 is formed as a continuous bottomed groove to have respectivecam groove portions for the first and second lens groups L1 and L2, andthat the first and second lens groups L1 and L2 are released from theconstraints of the three lens-drive cam grooves C1 at their respectiveaccommodation positions so that the first and second lens groups L1 andL2 can be accommodated to be positioned close to each other until thefirst lens group supporting frame 32 and the second lens group movingframe 31 come into contact with each other.

Namely, three follower pins 29 f which are projected radially outwardsfrom the first lens group moving frame 29 and three follower pins 31 fwhich are projected radially outwards from the second lens group movingframe 31 are slidably engaged in the three lens-drive cam grooves C1,respectively. Each lens-drive cam groove C1, which is formed as acontinuous bottomed groove, has a function to move the first and secondlens groups L1 and L2 in their respective zoom paths. Unlike the presentembodiment of the zoom lens barrel 10, in a conventional zoom lensbarrel having a cam ring for driving a plurality of movable lens groups,a set of cam grooves is necessary for each of the plurality of movablelens groups.

As shown in FIG. 20, each lens-drive cam groove C1 is provided at oneend thereof with an insertion end C1 e via which one of the threefollower pins 29 f of the first lens group moving frame 29 and one ofthe three follower pins 31 f of the second lens group moving frame 31are inserted into the lens-drive cam groove C1. Each lens-drive camgroove C1 is further provided with a first-lens-group zooming section(front lens group moving section) C1Z1, a second-lens-group zoomingsection (rear lens group moving section) C1Z2, a first-lens-groupaccommodation portion C1A1, a connecting portion C1A2 and asecond-lens-group-accommodation end portion C1S2, in that order from theinsertion end C1 e. The opposite ends (left and right ends as viewed inFIG. 20) of the first-lens-group zooming section C1Z1 determines atelephoto extremity Z1T and a wide-angle extremity Z1W of the first lensgroup L1, respectively. The opposite ends (left and right ends as viewedin FIG. 20) of the second-lens-group zooming section C1Z2 determines atelephoto extremity Z2T and a wide-angle extremity Z2W of the secondlens group L2, respectively. As shown in FIG. 20, in this particularembodiment of the zoom lens barrel 10, the angle of rotation of the camring 22 when driving each of the first and second lens group movingframes 29 and 31 from the accommodation position to the telephotoextremity is predetermined at 178 degrees, and the angle of rotation ofthe cam ring 22 when driving each of the first and second lens groupmoving frames 29 and 31 from the wide-angle extremity to the telephotoextremity is determined at 70 degrees.

As shown in FIG. 20, the width of the first-lens-group accommodationportion C1A1 of the lens-drive cam groove C1 in the optical axisdirection (the vertical direction as viewed in FIG. 20) is greater thanthe width of the other portions of the lens-drive cam groove C1 so thatthe associated follower pin 29 f can move freely in the first-lens-groupaccommodation portion C1A1. Namely, the first-lens-group accommodationportion C1A1 extends in a circumferential direction of the cam ring 22,and also widens in the optical axis direction to form a clearance forthe associated follower pin 29 f of the first lens group moving frame 29to be movable in the optical axis direction by an amount of movementcorresponding to the range of adjustment of the thread engagementposition of the male thread portion of the first lens group supportingframe 32 with respect to the female thread portion 29 d of the innerflange 29 g. The second-lens-group-accommodation end portion C1S2, whichis one end of the connecting portion C1A2 on the side opposite from thefirst-lens-group accommodation portion C1A1, is shaped to form aclearance for the associated follower pin 31 f of the second lens groupmoving frame 31 to be slightly movable both in the optical axisdirection and in a circumferential direction of the cam ring 22 when theassociated follower pin 31 f is engaged in thesecond-lens-group-accommodation end portion C1S2.

As shown in FIG. 16, which shows a developed view of the outerperipheral surface of the cam ring 22, the three engaging recesses 22 aof the cam ring 22 are formed so as not to interfere with the three camgrooves (second cam grooves) C2, which are formed on an outer peripheralsurface of the cam ring 22 so as to have a substantially V-shapedprofile (cam path) in a development view as shown in FIG. 16. The frontend of each engaging recess 22 a is positioned just behind an adjacentpeak (frontmost peak portion) C2E of the associated cam groove C2 whichis the frontmost portion of the cam groove C2. The front end of eachengaging recess 22 a is formed to have an oblique surface 22 a-1 so thateach engaging recess 22 a does not interfere with the associated camgrooves C2. The front end portion of each rotation-transmission arm 20 bis formed to have an oblique cutout portion 20 d which is shaped tocorrespond to the oblique surface 22 a-1 of the engaging recess 22 a(See FIG. 11B). Furthermore, as shown in FIG. 16, the three guide keys22 b are provided in the close vicinity of the three bayonet prongs 24,and are each formed so as to extend along an extension line Z whichextends parallel to the optical axis through the corresponding peak C2E.In other words, the three guide keys 22 b are each provided at acircumferential position of longest portion of a corresponding engagingrecess 22 a in a direction parallel to the optical axis. Accordingly,since the three guide keys 22 b can be made long in the directionparallel to the optical axis, the linear guidance precision thereof canbe increased.

The relative angular positions of the three follower pins 29 f and thethree follower pins 31 f about the optical axis O are determined so thateach follower pin 29 f and each follower pin 31 f are respectivelypositioned in the first-lens-group accommodation portion C1A1 and thesecond-lens-group-accommodation end portion C1S2 of the connectingportion C1A2 when the cam ring 22 is positioned in an accommodationposition thereof (see FIG. 20). The first-lens-group accommodationportion C1A1 and the second-lens-group-accommodation end portion C1S2 ofthe connecting portion C1A2, to some extent, do not constrain movementof the associated follower pins 29 f and 31 f, respectively. Namely,each follower pin 29 f and each follower pin 31 f can move in thefirst-lens-group accommodation portion C1A1 and thesecond-lens-group-accommodation end portion C1S2 of the connectingportion C1A2, respectively, in the optical axis direction because of theclearance formed between each groove portion and the associated followerpin. This clearance contributes to further miniaturization of the lengthof the zoom lens barrel 1 in an accommodation position thereof.

Since the three helical compression springs 30 press the first lensgroup moving frame 29 rearwards in the optical axis direction asdescribed above, the lens pressure ring 32 a that is supported by thefirst lens group moving frame 29, can retract up to a mechanicallycontacting point P (see FIG. 8) where the lens pressure ring 32 a comesin contact with the low-frictional ring sheet 38 that is fixed to thefront surface of the shutter pressure plate 37, due to the clearancebetween the first-lens-group accommodation portion C1A1 of eachlens-drive cam groove C1 of the cam ring 22 and the associated followerpin 29 f of the first lens group moving frame 29. Likewise, the flexiblePWB support member 31 j of the second lens group moving frame 31 canretract up to a mechanically contacting point Q (see FIG. 8) where thesecond lens group moving frame 31 comes in contact with the third lensframe 39 due to a clearance between the second-lens-group-accommodationend portion C1S2 of the connecting portion C1A2 of each lens-drive camgroove C1 of the cam ring 22 and the associated follower pin 31 f of thesecond lens group moving frame 31.

Due to such structures of the mechanically contacting points P and Q,the length of the zoom lens barrel 10 in an accommodation positionthereof is successfully reduced as compared with a conventional zoomlens barrel in which the respective accommodation positions of first andsecond lens groups which correspond to the first and second lens groupsL1 and L2 of the present embodiment of the zoom lens barrel areprecisely determined by associated cam grooves. Furthermore, as shown inFIG. 8, the third lens frame 39 can retract up to a mechanicallycontacting point R where the third lens frame 39 comes in contact withthe CCD holding frame 13 while compressing a helical compression spring42, which is fitted on the feed screw shaft 41 to be positioned betweenthe third lens frame 39 and the CCD holding frame 13 to bias the thirdlens frame 39 forward.

FIG. 8 shows an accommodation position of the zoom lens barrel 10 wherethe first lens group moving frame 29 (lens pressure ring 32 a) is incontact with the low-frictional ring sheet 38, where the second lensgroup moving frame 31 is in contact with the third lens frame 39, andwhere the third lens frame 39 is in contact with the CCD holding frame13.

The amount of rearward movement of the first lens group moving frame 29relative to the second lens group moving frame 31 depends on theposition of the first lens group supporting frame 32 relative to thefirst lens group moving frame 29, since the position of the second lensgroup supporting frame 32 relative to the first lens group moving frame29 varies by an adjustment of the thread engagement position of the malethread portion of the first lens group supporting frame 32 with respectto the female thread portion 29 d of the inner flange 29 g duringassembly. Such a variation due to the adjustment is absorbed byextension or compression of the helical compression springs 30 so thatthe zoom lens barrel 10 can be accommodated with the lens pressure ring32 a, the second lens group moving frame 31, and the third lens frame 39being in contact with the low-frictional ring sheet 38, the third lensframe 39, and the CCD holding frame 13 at the mechanically contactingpoints P, Q and R, respectively.

If the cam ring 22 rotates in a direction from the accommodationposition toward a photographing position in the zooming groove portion11 a 4, each follower pin 29 f of the first lens group moving frame 29which is engaged in the first-lens-group accommodation portion C1A1moves from the first-lens-group accommodation portion C1A1 to thefirst-lens-group zooming section C1Z1 via the second-lens-group zoomingsection C1Z2, while each follower pin 31 f of the second lens groupmoving frame 31 which is engaged in the connecting portion C1A2 movesfrom the connecting portion C1A2 to the second-lens-group zoomingsection C1Z2 via the first-lens-group accommodation portion C1A1.Accordingly, the second-lens-group zooming sections C1Z2 of the threelens-drive cam grooves C1 that are used for driving the three followerpins 31 f of the second lens group moving frame 31 are used as merepassing sections for the three follower pins 29 f of the first lensgroup moving frame 29 via which the three follower pins 29 f move fromthe first-lens-group accommodation position to the photographingposition. The above-described structure which provides such passingsections is advantageous to reduce the number of cam grooves which areto be formed on the cam ring 22, which is in turn advantageous to reducethe angle of inclination of each cam groove with respect to acircumferential direction of the cam ring 22.

The first ring 28 moves in the optical axis direction independent of thefirst lens group moving frame 29 in a moving path which is substantiallythe same as the moving path of the first lens group moving frame 29.Accordingly, the cam ring 22 is provided, on an outer peripheral surfaceat equi-intervals (intervals of 120 degrees) in a circumferentialdirection thereof, with the three cam grooves C2 (see FIGS. 16 through19). The first ring 28 is provided, on an inner peripheral surface atequi-intervals in a circumferential direction thereof, with threefollower pins 28 f which are slidably engaged in the three cam groovesC2 of the cam ring 22, respectively. The profiles of the cam grooves C2resemble those of the lens-drive cam grooves C1. As shown in FIG. 17A,each cam groove C2 is provided at one end thereof with an insertion endC2 e via which one of the three follower pins 28 f of the first ring 28is inserted into the cam groove C2. Each cam groove C2 is furtherprovided with a first section C2Z1 which corresponds to thefirst-lens-group zooming section C1Z1, a second section C2Z2 whichcorresponds to the second-lens-group zooming section C1Z2, and a barrierdrive section C2B. The barrier drive section C2B extends in acircumferential direction of the cam ring 22, so that the cam ring 22rotates about the optical axis O without moving in the optical axisdirection relative to the first ring 28 as long as each follower pin 28f is engaged in the barrier drive section C2B. As shown in FIG. 16, inthis particular embodiment of the zoom lens barrel 10, the angle ofrotation of the cam ring 22 when driving the first ring 28 from theaccommodation position to the telephoto extremity is predetermined at178 degrees, and the angle of rotation of the cam ring 22 when drivingthe first ring 28 from the wide-angle extremity to the telephotoextremity is determined at 70 degrees.

By providing the first ring 28, which extends forward so that an outerperipheral surface thereof is exposed to the outside of the zoom lensbarrel 10, as an element separate from the first lens group moving frame29, and by guiding the first ring 28 in the optical axis direction via acam mechanism independent of the first lens group moving frame 29 asdescribed above, external forces applied to the first ring 28 can beprevented from being transferred to the first lens group L1 via thefirst lens group moving frame 29, which in turn prevents deteriorationin optical performance of the zoom lens barrel 10 due to eccentricity ofthe optical axis of the first lens group L1. In addition, the structureof the cam ring 22 wherein the three lens-drive cam grooves C1 and thethree cam grooves C2, whose cam profiles are similar (though differingslightly in shape) to each other, are formed on the cam ring 22 inslightly different positions thereon in the optical axis direction doesnot increase the wall thickness of the cam ring 22. Moreover, externalforces applied to the first ring 28 rearward in the optical axisdirection can be received by the first lens group moving frame 29 viathe three follower pins 29 f.

Furthermore, since the three follower pins 28 f, which are respectivelyengaged in the three cam grooves C2, and the three follower pins 29 f,which are respectively engaged in the three lens-drive cam grooves C1,are respectively aligned side by side in a direction parallel to theoptical axis O, the strength of the spring force of the three helicalcompression springs 30 that are held between the first ring 28 and thefirst lens group moving frame 29 to bias the first ring 28 and the firstlens group moving frame 29 in opposite directions away from each othervaries little even if the cam ring 22 rotates relative to the first ring28 and the first lens group moving frame 29.

As shown in FIG. 1, the barrier unit 43 includes a barrier blade supportfront plate 45, a pair of barrier blades 46, two torsion springs 47 anda barrier blade support rear plate 48, and is fixed to the front end ofthe first ring 28 to be positioned therein, in front of the inner flange28 b. The barrier drive ring 44 is positioned in the first ring 28 andheld between the barrier unit 43 and the inner flange 28 b of the firstring 28 to be rotatable freely about the optical axis O. The cam ring 22is provided at the front end thereof with three recesses 22 k (see FIGS.16 through 20). The barrier drive ring 44 is provided on an outerperipheral surface thereof with three engaging portions 44 a. The camring 22 is provided at one end of each recesses 22 k with a rotationtransfer face 22 d which extends parallel to the optical axis O andextends through a corresponding circumferential slot 28 z (see FIG. 1)formed on the inner flange 28 b of the first ring 28. As shown in FIGS.16 through 20, the three recesses 22 k are formed on the cam ring 22 atportions thereon other than the portions where the three cam grooves C2are formed.

As shown in FIG. 1, the barrier unit 43, which includes the barrierblade support front plate 45, the pair of barrier blades 46, the twotorsion springs 47 and the barrier blade support rear plate 48, isformed as a single assembly in advance. The barrier blade support frontplate 45 is provided at the center thereof with a photographing aperture45 a, and is further provided, on a rear surface thereof on oppositesides of the photographing aperture 45 a, with two bosses (not shown),respectively, which extend rearwards. Each barrier blade 46 is providedat one end thereof with a hole in which one of the two bosses is engagedso that each barrier blade 46 is rotatable about the associated boss.The two torsion springs 47 bias the pair of barrier blades 46 to rotatein opposite rotational directions to shut the pair of barrier blades 46,respectively. The pair of barrier blades 46 are supported between thebarrier blade support front plate 45 and the barrier blade support rearplate 48. The barrier blade support rear plate 48 is provided at thecenter thereof with a central aperture which is aligned with thephotographing aperture 45 a in the optical axis direction, and isfurther provided on opposite sides of the central aperture with twoslots 48 a. Each barrier blade 46 is provided in the vicinity of theassociated boss with an engaging projection 46 a (only one of whichappears in FIGS. 8 through 10) which extends rearward, toward thebarrier drive ring 44, to pass through the associated slot 48 a of thebarrier blade support rear plate 48.

The barrier drive ring 44 is biased to rotate in a direction to open thepair of barrier blades 46 by a helical extension spring 49 whoseopposite ends are hooked on an engaging projection 44 b formed on thebarrier drive ring 44 and an engaging projection 28 h formed on a frontsurface of the inner flange 28 b of the first ring 28. The spring forceof the helical extension spring 49 is greater than the total springforce of the two torsion springs 47. The two drive projections 44 c ofthe barrier drive ring 44 come into contact with the two engagingprojections 46 a of the pair of barrier blades 46 to open the pair ofbarrier blades 46, respectively, when the barrier drive ring 44 is in afully rotated position thereof due to the spring force of the helicalextension spring 49. If the barrier drive ring 44 is rotated in adirection to close the pair of barrier blades 46 against the springforce of the helical extension spring 49, the two drive projections 44 crespectively move away from the two engaging projections 46 a of thepair of barrier blades 46 so that the pair of barrier blades 46 areclosed by the spring force of the two torsion springs 47.

The three rotation transfer faces 22 d of the cam ring 22 respectivelycome into contact with the three engaging portions 44 a of the barrierdrive ring 44 to press the three engaging portions 44 a against thespring force of the helical extension spring 49 to rotate the barrierdrive ring 44. When the cam ring 22 is in the accommodation positionthereof, the three rotation transfer faces 22 d are respectively incontact with the three engaging portions 44 a of the barrier drive ring44 via the three circumferential slots 28 z formed on the inner flange28 b of the first ring 28. The barrier drive ring 44 is rotated aboutthe optical axis O against the spring force of the helical extensionspring 49 to close the pair of barrier blades 46. If the cam ring 22rotates about the optical axis O in a barrier opening direction(counterclockwise as viewed from the front of the zoom lens barrel 10)with respect to the first ring 28, with the three follower pins 28 fbeing respectively engaged within the barrier drive sections C2B of thethree cam grooves C2 of the cam ring 22, the three rotation transferfaces 22 d are respectively disengaged from the three engaging portions44 a of the barrier drive ring 44 so that the barrier drive ring 44 isrotated in a direction to open the pair of barrier blades 46 by thespring force of the helical extension spring 49.

The barrier unit 43 having the above described structure is fitted intothe front end opening of the first ring 28 from the front thereof. Thebarrier blade support front plate 44 is provided on an outer peripheraledge thereof with a plurality of engaging portions which arerespectively engaged with a corresponding plurality of hooks (not shown)formed on an inner peripheral surface of the front end opening of thefirst ring 28 to prevent the barrier unit 43 from coming off the frontof the first ring 28. The barrier drive ring 44 is held between thebarrier unit 43 and the inner flange 28 b of the first ring 28 to berotatable about the optical axis O.

As has been described above, the zooming groove portion 11 a 4 (see FIG.28) of each cam groove 11 a of the stationary barrel 11 extends in acircumferential direction of the stationary barrel 11 and does notextend in the optical axis direction. Therefore, the cam ring 22 rotatesabout the optical axis O without moving in the optical axis directionwhen the three follower pins 22 f of the cam ring 22 and the threefollower pins 21 f of the biasing ring 21 follow the three zoominggroove portions 11 a 4 of the three cam grooves 11 a in the zoomingsection, respectively. In the zooming section that is determined by thezooming groove portion 11 a 4, it is necessary to remove backlash andplay between the three follower pins 22 f and the zooming grooveportions 11 a 4 of the three cam grooves 11 a.

To remove such backlash and play, each of the three follower pins 21 fand the associated one of the three follower pins 22 f are engaged in acommon cam groove of the three cam grooves 11 a of the stationary barrel11 at slightly different circumferential positions as shown in FIG. 28,and each follower pin 21 f of the biasing ring 21 and each follower pin22 f of the cam ring 22 are pressed against a rear side edge of theassociated cam groove 11 a and a front side edge of the same cam groove11 a, respectively, by the spring force of the three compression helicalsprings 26. Due to this structure wherein the three follower pins 22 fof the cam ring 22 are pressed against the front side edges of thezooming groove portion 11 a 4 of the three cam grooves 11 a when engagedin the zooming groove portion 11 a 4, backlash and play between thethree follower pins 22 f and the zooming groove portions 11 a 4 of thethree cam grooves 11 a are removed.

In addition to the above described structures wherein the three linearguide grooves 29 c are formed on an inner peripheral surface of thefirst lens group moving frame 29 while the three linear guide keys 31 a,which are respectively engaged in the three linear guide grooves 29 c,are formed on an outer peripheral surface of the second lens groupmoving frame 31, three circumferential recesses 29 h (see FIGS. 21Athrough 21J) are formed on the first lens group moving frame 29 at thefront ends of the three linear guide grooves 29 c, respectively. Eachcircumferential recess 29 h allows the associated linear guide key 31 aof the second lens group moving frame 31 to move therein in acircumferential direction about the optical axis O, i.e., allows thesecond lens group moving frame 31 to rotate about the optical axis Orelative to the first lens group moving frame 29 in a rangecorresponding to the circumferential length of the circumferentialrecess 29 h. The second lens group moving frame 31 can rotate about theoptical axis O relative to the first lens group moving frame 29 alongthe three circumferential recesses 29 h only when the second lens groupmoving frame 31 is in the vicinity of the accommodation positionthereof.

Note that the first lens group moving frame 29 is provided on the innerflange 29 g thereof with three circumferential slots 29 j (see FIGS. 24through 27). The second lens group moving frame 31 is provided at thefront end thereof with three front projecting portions 31 g onrespective outer surfaces on which the three linear guide keys 31 a areformed, respectively. When each linear guide key 31 a is positioned inthe associated circumferential recess 29 h, i.e., when the second lensgroup L2 is in the vicinity of the accommodation position thereof, thethree front projecting portions 31 g of the second lens group movingframe 31 extend through the inner flange 29 g of the first lens groupmoving frame 29 to project forward from the inner flange 29 g via thethree circumferential slots 29 j, respectively. Accordingly, allowingthe three linear guide keys 31 a to project forward from the innerflange 29 g through the three circumferential slots 29 j, respectively,achieves the short length of the zoom lens barrel 10 in an accommodationposition shown in FIG. 8.

In a state where the zoom lens barrel 10 is in an accommodationposition, i.e., where each of the three follower pins 29 f of the firstlens group moving frame 29 is engaged in the first-lens-groupaccommodation portion C1A1 of the associated lens-drive cam groove C1 asshown in FIG. 21A, a rotation of the cam ring 22 in a direction toextend the zoom lens barrel 10 (in a direction indicated by an arrow “X”in FIGS. 21A through 21J, i.e., counterclockwise as viewed from thefront of the zoom lens barrel 10) causes each follower pin 29 f of thefirst lens group moving frame 29 to move slightly from thefirst-lens-group accommodation portion C1A1 toward the second-lens-groupzooming section C1Z2 of the associated lens-drive cam groove C1 as shownin FIG. 21B. At this time, each follower pin 31 f of the second lensgroup moving frame 31 does not move out from thesecond-lens-group-accommodation end portion C1S2 of the connectingportion C1A2.

Further rotational movement of the cam ring 22 in the same direction Xcauses each follower pin 29 f of the first lens group moving frame 29 tofurther move slightly toward the second-lens-group zooming section C1Z2while moving rearward slightly in the optical axis direction as shown inFIG. 21C. At the same time, since each follower pin 31 f does not moveout from the second-lens-group-accommodation end portion C1S2 of theconnecting portion C1A2, front end surfaces (upper end surfaces asviewed in FIG. 21C) of the three cutout portions 29 i of the second lensgroup moving frame 29 come into contact with front end surfaces of thethree engaging projections 31 h of the second lens group moving frame31, respectively, as shown in FIG. 21C.

Further rotational movement of the cam ring 22 in the same direction Xcauses each follower pin 29 f of the first lens group moving frame 29 tofurther move slightly toward the second-lens-group zooming section C1Z2while moving rearward (downward as viewed in FIG. 21D) in the opticalaxis direction so that the front end surfaces of the three cutoutportions 29 i press the three engaging projections 31 h rearward in theoptical axis direction, respectively, to move each follower pin 31 f ofthe second lens group moving frame 31 in the connecting portion C1A2from the second-lens-group-accommodation end portion C1S2 thereof towardthe first-lens-group accommodation portion C1A1 as shown in FIG. 21D.

Further rotational movement of the cam ring 22 in the same direction Xcauses each follower pin 29 f of the first lens group moving frame 29 tomove forward in the second-lens-group zooming section C1Z2 in a leftoblique direction with respect to the cam ring 22 as viewed in FIG. 21E,so that the three cutout portions 29 i are respectively disengaged fromthe three engaging projections 31 h, and at the same time, rear endsurfaces of the three circumferential recesses 29 h respectively comeinto contact with rear end surfaces of the three linear guide keys 31 aas shown in FIG. 21E.

Further rotational movement of the cam ring 22 in the same direction Xcauses each follower pin 29 f of the first lens group moving frame 29 tofurther move forward in the second-lens-group zooming section C1Z2 inthe same left oblique direction with respect to the cam ring 22 so thatthe rear end surfaces of the three circumferential recesses 29 hrespectively press the rear end surfaces of the three linear guide keys31 a rearward in the optical axis direction, to thereby move eachfollower pin 31 f of the second lens group moving frame 31 in theconnecting portion C1A2 back toward the second-lens-group-accommodationend portion C1S2 thereof as shown in FIG. 21F. At this time, each linearguide keys 31 a of the second lens group moving frame 31 is positionedin the associated linear guide groove 29 c of the first lens groupmoving frame 29 in the vicinity of the front end thereof.

During the time the zoom lens barrel 10 moves from the position shown inFIG. 21A to the position shown in FIG. 21F, each linear guide keys 31 aof the second lens group moving frame 31 rotates in the associatedcircumferential recess 29 h in a circumferential direction of the firstlens group moving frame 29 with respect to the first lens group movingframe 29. Rotating the second lens group moving frame 31 with respect tothe first lens group moving frame 29 in such a manner makes it possiblefor the first lens group moving frame 29 to move forward smoothlywithout interfering with the second lens group moving frame 31. Thesecond lens group moving frame 31 rotates about the optical axis O withrespect to the first lens group moving frame 29 by 39 degrees (see FIG.20) when the zoom lens barrel 10 moves from the position shown in FIG.21A to the position shown in FIG. 21F.

Further rotational movement of the cam ring 22 in the same direction Xcauses each follower pin 29 f of the first lens group moving frame 29 tofurther move forward in the second-lens-group zooming section C1Z2 inthe same left oblique direction with respect to the cam ring 22 so thateach linear guide keys 31 a of the second lens group moving frame 31 isproperly engaged in the associated linear guide groove 29 c as shown inFIG. 21G. Thereafter, the first lens group moving frame 29 and thesecond lens group moving frame 31 are prohibited from rotating relativeto each other, while each follower pin 29 f and the associated one ofthe three follower pins 31 f move in the associated one of the threelens-drive cam grooves C1 in a direction to the left as viewed in FIG.21G while maintaining a space between the follower pin 29 f and thefollower pin 31 f in a circumferential direction.

Subsequently, if the cam ring 22 continues to rotate in the direction Xwith each linear guide keys 31 a of the second lens group moving frame31 being engaged in the associated linear guide groove 29 c of the firstlens group moving frame 29, the first lens group moving frame 29 and thesecond lens group moving frame 31 move linearly in the optical axisdirection without rotating about the optical axis O while changing aspace in the optical axis therebetween by the movement of the threefollower pins 29 f and the three follower pins 31 f in the threelens-drive cam grooves C1 in a direction toward the left as shown inFIGS. 21H through 21I. Consequently, each follower pin 29 f and theassociated one of the three follower pins 31 f reach their respectivewide-angle extremities in the associated one of the three lens-drive camgrooves C1 as shown in FIG. 21J.

Although not shown in the drawings, each follower pin 29 f and theassociated one of the three follower pins 31 f reach their respectivetelephoto extremities in the associated one of the three lens-drive camgrooves C1 while maintaining a space therebetween in a circumferentialdirection if the cam ring 22 further continues rotating in the samedirection X.

On the other hand, in a state where the zoom lens barrel 10 is in aphotographing position, if the cam ring 22 rotates in a direction toretract the zoom lens barrel 10, i.e., in a direction opposite to thedirection X, each follower pin 29 f and each follower pin 31 f move inan order reverse to the above described order, and return to thefirst-lens-group accommodation portion C1A1 and the connecting portionC1A2, respectively.

FIG. 22 is a graph showing variations of the angle of rotation of thesecond lens group moving frame 31 with respect to the cam ring 22 from astate where the second lens group moving frame 31 is in an accommodationposition to a state immediately after the three linear guide keys 31 aare respectively engaged in the three linear guide grooves 29 c, i.e.,from the position shown in FIG. 21A to the position shown in FIG. 21F.FIG. 23 is a graph showing the relationship between the amount ofdisplacement of the first lens group moving frame 29 from theaccommodation position thereof (represented by “0” in FIG. 23) in theoptical axis direction and the angle of rotation of the cam ring 22, andfurther showing the relationship between the amount of displacement ofthe second lens group moving frame 31 from the accommodation positionthereof (represented by “0” in FIG. 23) in the optical axis directionand the angle of rotation of the cam ring 22. In each of FIGS. 22 and23, (a), (b), (c), (d), (e) and (f) represent the rotational angles ofthe cam ring 22 in FIGS. 21A, 21B, 21C, 21D, 21E and 21F, respectively.The term “Limit Angle” shown in each of FIGS. 22 and 23 represents aspecific angle of rotation of the cam ring 22, wherein the first andsecond lens group moving frames 29 and 31 cannot reach their respectivetelephoto extremities when the three linear guide keys 31 a do not enterthe associated linear guide groove 29 c by the time the cam ring 22 hasrotated to the specific angle of rotation of the cam ring 22.

When the first and second lens group moving frames 29 and 31 rotaterelative to each other at their respective accommodation positions,friction (frictional resistance) is produced between the lens pressurering 32 a, which is supported by the first lens group moving frame 29,and the front surface of the shutter pressure plate 37, which issupported by the second lens group moving frame 31 via the shutter unit36, if a low-frictional element such as the low-frictional ring sheet 38is not fixed to the front surface of the shutter pressure plate 37,unlike the present invention. Namely, there is a possibility of theaxial position of the first lens group supporting frame 32 deviatingfrom the correct position thereof due to rotation thereof which can becaused by friction since the first lens group supporting frame 32 iscoupled to the first lens group moving frame 29 via the threadengagement of the male thread portion of the first lens group supportingframe 32 with the female thread portion 29 d of the inner flange 29 g ofthe first lens group moving frame 29. Nevertheless, in the presentembodiment of the zoom lens barrel, such friction is not produced evenif the first and second lens group moving frames 29 and 31 rotaterelative to each other at their respective accommodation positionsbecause the low-frictional ring sheet 38 is fixed to the front surfaceof the shutter pressure plate 37.

The overall movement of the zoom lens barrel 10, having the abovedescribed structure, from the accommodation position to a photographingposition (a position in the zooming section) will be hereinafterdiscussed.

When the zoom lens barrel 10 is in an accommodation position, the firstlens group supporting frame 32 which is supported by the first lensgroup moving frame 29, which is biased rearward by the three helicalcompression springs 30, is retracted to the above described mechanicallycontacting point P, where the lens pressure ring 32 a comes in contactwith the low-frictional ring sheet 38 due to the clearance between thefirst-lens-group accommodation portion C1A1 and the associated followerpin 29 f of the first lens group moving frame 29. The second lens groupmoving frame 31 is also retracted to the above described mechanicallycontacting point Q, where the second lens group moving frame 31 comes incontact with the third lens frame 39 due to the clearance between thesecond-lens-group-accommodation end portion C1S2 and the associatedfollower pin 31 f of the second lens group moving frame 31. Furthermore,the third lens frame 39 is retracted to the above described mechanicallycontacting point R, where the third lens frame 39 comes in contact withthe CCD holding frame 13 against the spring force of the helicalcompression spring 42 with the helical compression spring 42 being in acompressed (contracted) state. With these three mechanical contacts atthe mechanically contacting points P, Q and R, the length of the zoomlens barrel 10 in an accommodation position is successfully reduced.When the zoom lens barrel 10 is in an accommodation position, the pairof barrier blades 46 are closed to shut the photographing aperture 45 a,since the three rotation transfer faces 22 d respectively press thethree engaging portions 44 a of the barrier drive ring 44 against thespring force of the helical extension spring 49 to rotate the barrierdrive ring 44 in a direction to move the two drive projections 44 c awayfrom the two engaging projections 46 a of the pair of barrier blades 46,respectively.

In the accommodation position of the zoom lens barrel 10, when therotational ring 20 rotates in a direction to extend the zoom lens barrel10 relative to the stationary barrel 11, the cam ring 22, which isprovided with the three follower pins 22 f, and the biasing ring 21,which is provided with the three follower pins 21 f, rotate about theoptical axis O in accordance with the cam profile of the accommodationgroove portion 11 a 2 of each of the three cam grooves 11 a that areformed on an inner peripheral surface of the stationary barrel 11 (seeFIG. 28). This rotational movement of the cam ring 22 causes eachfollower pin 29 f and the associated follower pin 31 f, which arerespectively engaged in the first-lens-group accommodation portion C1A1of the associated lens-drive cam groove C1 and thesecond-lens-group-accommodation end portion C1S2 of the same lens-drivecam groove C1, to vary the relative position between the follower pin 29f and the follower pins 31 f in a circumferential direction of the camring 22 without varying the position of each of the follower pin 29 fand the follower pins 31 f relative to the cam ring 22 in the opticalaxis direction (see the transition from (a) to (b) in FIG. 23).Thereafter, each follower pin 21 f of the biasing ring 21 and eachfollower pin 22 f of the cam ring 22 enter the position-changing grooveportion 11 a 3, so that the cam ring 22 together with the biasing ring21 moves forward in the optical axis direction while rotating about theoptical axis O. This causes the second lens group moving frame 31 todisengage from the third lens frame 39, and almost at the same time,each follower pin 29 f of the first lens group moving frame 29 startsmoving rearward in the optical axis direction with respect to the camring 22 (see (b) in FIG. 23). As a result, the first lens group movingframe 29 presses the second lens group moving frame 31 rearward in theoptical axis direction to move the second lens group moving frame 31slightly in the rearward direction. The displacement of the second lensgroup moving frame 31 at this time is very small, and thus is not shownin FIG. 23. In an early stage of this rotation of the cam ring 22 by theposition-changing groove portions 11 a 3 of the stationary barrel 11,the three rotation transfer faces 22 d of the cam ring 22 arerespectively disengaged from the three engaging portions 44 a of thebarrier drive ring 44 so that the barrier drive ring 44 is rotated in adirection to open the pair of barrier blades 45 by the spring force ofthe helical extension spring 49 against the spring force of the twotorsion springs 47. Meanwhile, the second lens group moving frame 31rotates about the optical axis O relative to the first lens group movingframe 29 so that the lens pressure ring 32 a fixed to the first lensgroup supporting frame 32 rotatably slides on the low-frictional ringsheet 38 before and after the opening operation of the pair of barrierblades 46.

Subsequently, further forward movement of each follower pin 21 f of thebiasing ring 21 and each follower pin 22 f of the cam ring 22 in theposition-changing groove portion 11 a 3 (see FIG. 28) causes the secondlens group moving frame 31 to start moving rearward in the optical axisdirection (see (c) in FIG. 23). Thereafter, the first and second lensgroup moving frames 29 and 31 move rearward in the optical axisdirection with respect to the cam ring 22 as shown in FIG. 23 (see (c)and (d) in FIG. 23). Subsequently, the mechanical contact between thefirst and second lens group moving frames 29 and 31 is released at thetime the first lens group moving frame 29 moves forward in the opticalaxis direction (see (d) and (e) in FIG. 23). Subsequently, themechanical contact between the second lens group moving frame 31 and thethird lens frame 39 is released, and thereafter each of the three linearguide keys 31 a is engaged in the associated one of the four linearguide grooves 29 c (see (f) in FIG. 23).

Thereafter, the first and second lens group moving frames 29 and 31 moveto the respective wide-angle extremities thereof in the optical axisdirection while maintaining the circumferential space therebetween untileach follower pin 21 f and each follower pin 22 f reach the respectivewide-angle extremities thereof in the zooming groove portion 11 a 4 ofthe associated one of the three cam grooves 11 a that are formed on theinner peripheral surface of the stationary barrel 11 (see FIGS. 21Fthrough 21J).

Further rotation of the rotational ring 20 causes each follower pin 21 fof the biasing ring 21 and each follower pin 22 f of the cam ring 22 tomove from the respective wide-angle extremities in the zooming grooveportion 11 a 4 toward the respective telephoto extremities, so that thecam ring 22 rotates about the optical axis O without moving in theoptical axis direction. At this stage, if the cam ring 22 rotates in thezooming range (i.e., if each follower pin 29 f and each follower pin 31f move in the first-lens-group zooming section C1Z1 and thesecond-lens-group zooming section C1Z2, respectively), the first andsecond lens group moving frames 29 and 31 (the first and second lensgroups L1 and L2) move in the optical axis direction in accordance withthe cam profiles of the first-lens-group zooming section C1Z1 and thesecond-lens-group zooming section C1Z2, to thereby vary the focal lengthof the photographing optical system, i.e., to perform a zoomingoperation. This zooming operation is carried out by manually operating aconventional zoom switch or knob (not shown). Immediately after arelease button is depressed, the aforementioned step motor (not shown),which drives the feed screw shaft 41 to move the third lens group L3(the third lens frame 39), rotates by an amount of rotationcorresponding to information on a photographing distance to move thethird lens group L3 to bring an object into focus. The shutter unit 36drives the shutter blades 36 a (see FIGS. 8, 9 or 10) to open and closein accordance with the information on the object brightness.

Backlash and play between the three follower pins 21 f of the biasingring 21, the three follower pins 22 f of the cam ring 22 and the zoominggroove portions 11 a 4 of the three cam grooves 11 a of the stationarybarrel 11 are removed at the time the motor 18 stops during the timeeach of the three follower pins 21 f and the associated one of the threefollower pins 22 f are moving in the zooming groove portion 11 a 4 ofthe associated one of the three cam grooves 11 a, since each followerpin 21 f of the biasing ring 21 and the associated one of the threefollower pins 22 f of the cam ring 22 are pressed against a rear sideedge of the associated cam groove 11 a and a front side edge of the samecam groove 11 a, respectively, over the full range of the cam groove 11a by the spring force of the three compression helical springs 26 asdescribed above.

When the first lens group moving frame 29 moves linearly in the opticalaxis direction, the first ring 28 also moves in the optical axisdirection without varying the position thereof relative to the firstlens group moving frame 29 due to the engagement of the three followerpins 28 f with the three cam grooves C2 of the cam ring 22, the profilesof which are similar to those of the lens-drive cam grooves C1. At thesame time, the first ring 28 and the second ring 27, the respectiveouter peripheral surfaces of which are exposed to the outside of thezoom lens barrel 10, move together in the optical axis direction sincethe second ring 27 moves together with the cam ring 22 in the opticalaxis direction at all times due to the engagement of the three bayonetprongs 27 c of the second ring 27 with the three bayonet prongs 24 ofthe cam ring 22.

On the other hand, when the cam ring 22 rotates in a direction from thezooming section via the preparation section (i.e., in the barrierclosing direction), the first and second rings 28 and 27 retracttogether in the optical axis direction by operations reverse to theabove described operations. Subsequently, the first lens group movingframe 29, which supports the first lens group L1, and the second lensgroup moving frame 31, which supports the second lens group L2, comeinto contact with each other at their respective rear ends via the threehelical compression springs 30. Subsequently, the second lens groupmoving frame 31 retreats until coming into contact with the third lensframe 39. Subsequently, the second lens group moving frame 31 furtherretreats until the third lens frame 39 comes into contact with the CCDholding frame 13 against the spring force of the helical compressionspring 42, which biases the third lens frame 39 forward. At the sametime, the three rotation transfer faces 22 d respectively press thethree engaging portions 44 a of the barrier drive ring 44 against thespring force of the helical extension spring 49 to rotate the barrierdrive ring 44 in a direction to close the pair of barrier blades 46 toshut the photographing aperture 45 a.

In the present embodiment of the zoom lens barrel 10, as describedabove, the diameter of the rotational ring 20, which is positioned inthe stationary barrel 11, can be reduced to the same size as thediameter of the cam ring 22 because the cam ring 22 is provided on anouter peripheral surface thereof with the three engaging recesses 22 a,which are shaped to substantially correspond to the threerotation-transmission arms 20 b and each of which has a radial depth thesame as the radial thickness of each rotation-transmission arm 20 b, andbecause the three rotation-transmission arms 20 b are engaged in thethree engaging recesses 22 a through the three slots S that are formedradially inside the annular wall 23, respectively (See FIGS. 12 through15). Consequently, the diameters of the first and second rings 28 and 27can be reduced, which in turn makes it possible to reduce the size ofthe zoom lens barrel 10, especially the diameter thereof. Moreover, thethree rotation-transmission arms 20 b are prevented from coming off thethree engaging recesses 22 a radially outwards, respectively, by theannular wall 23, which forms the three slots S, and the three bayonetprongs 24.

In the present embodiment of the zoom lens barrel 10, rotation of themotor 18 is transferred from the rotational ring 20 to the cam ring 22with efficiency since the three rotation-transmission arms 20 b areengaged in the three engaging recesses 22 a, respectively. Moreover,rotation of the motor 18 is transferred from the rotational ring 20 tothe cam ring 22 with reliability because three rotation-transmissionarms and corresponding three engaging recesses are formed on therotational ring 20 and the cam ring 22 to serve as the threerotation-transmission arms 20 b and the three engaging recesses 22 a,respectively.

Furthermore, the three rotation-transmission grooves 20 c and the threeguide keys 22 b, which serve as elements for transferring rotation ofthe motor 18 from the rotational ring 20 to the cam ring 22, also serveas linear guide elements for guiding the cam ring 22 so as to movable inthe optical axis direction with respect to the rotational 20 (therotational ring being prevented from moving in the optical axisdirection), which contributes to a reduction of the number of elementsof the zoom lens barrel 10.

Furthermore, the three bayonet prongs 24, which are respectively engagedwith the three bayonet prongs 27 c of the second ring 27, are formed onthe annular wall 23 which serves as a member for preventing the threerotation-transmission arms 20 b from coming off the three engagingrecesses 22 a, and also contributes to a reduction of the number ofelements of the zoom lens barrel 10.

Although each rotation-transmission arm 20 b is provided with therotation-transmission groove 20 c while the cam ring 22 is provided withthe three guide keys 22 b, each of which is engaged in the associatedrotation-transmission groove 20 c in the above described embodiment ofthe zoom lens barrel 10, each rotation-transmission arm 20 b can beprovided with a guide key corresponding to each guide key 22 b while thecam ring 22 can be provided with a rotation-transmission groovecorresponding to each rotation-transmission groove 20 c.

The present invention can be applied not only to a zoom lens barrel butalso to a fixed-focal-length lens barrel.

As can be understood from the above description, according to thepresent invention, a compact and small-diameter lens barrel including acam ring and a rotational ring wherein the cam ring moves along anoptical axis while rotating about the optical axis by rotation of thecam ring is achieved.

Obvious changes may be made in the specific embodiment of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

What is claimed is:
 1. A lens barrel comprising: a cam ring which isrotated about an optical axis to move at least one lens group in theoptical axis direction via at least one cam groove formed on said camring; and a rotational ring which transfers a rotational motion to saidcam ring; wherein said rotational ring includes at least onerotation-transmission arm extending in said optical axis direction;wherein said cam ring comprises: at least one bottomed engaging recesswhich is formed on an outer peripheral surface of said cam ring, and inwhich said rotation-transmission arm is slidably inserted to berelatively movable in said optical axis direction; and an outer flangeformed on an outer peripheral surface of said cam ring to form a slotwhich penetrates therethrough in said optical axis direction betweensaid outer flange and a bottom radial surface of said engaging recess sothat said rotation-transmission arm is slidably inserted in saidengaging recess through said slot.
 2. The lens barrel according to claim1, wherein the shape of said engaging recess substantially correspondsto said rotation-transmission arm, and wherein a radial depth of saidengaging recess is substantially the same as a radial thickness of saidrotation-transmission arm.
 3. The lens barrel according to claim 1,wherein said cam ring is movable in said optical axis direction withrespect to said rotational ring, said rotation-transmission arm and saidengaging recess are slidably engaged to be movable in the optical axisdirection.
 4. The lens barrel according to claim 3, wherein saidrotational ring is prevented from moving in said optical axis direction.5. The lens barrel according to claim 3, further comprising a stationarybarrel positioned around said cam ring and including at least onecam-ring guiding cam groove formed on an inner peripheral surfacethereof; wherein said cam ring is rotated about said optical axis whilemoving in said optical axis direction in accordance with a profile ofsaid cam-ring guiding cam groove.
 6. The lens barrel according to claim5, wherein said rotational ring is positioned in said stationary barrelso as to be rotatable about said optical axis without moving in saidoptical axis direction with respect to said stationary barrel.
 7. Thelens barrel according to claim 1, further comprising a movable ringpositioned around said cam ring, said movable ring being movable in saidoptical axis direction, and a plurality of first bayonet prongs beingformed on said movable ring; wherein said outer flange includes aplurality of second bayonet prongs which are engaged with said pluralityof first bayonet prongs so that said cam ring and said movable ring movetogether in said optical axis direction.
 8. The lens barrel according toclaim 7, further comprising another movable ring positioned between saidcam ring and said movable ring, wherein each of said movable ring andsaid another movable ring is guided linearly in said optical axisdirection without rotating about said optical axis, and wherein saidanother movable ring projects forward from a front end of said movablering when said lens barrel is in operation.
 9. The lens barrel accordingto claim 1, further comprising a motor which generates said rotationalmotion, so that said rotational ring transfers said rotational motionfrom said motor to said cam ring.
 10. The lens barrel according to claim1, wherein said lens group comprises two movable lens groups; andwherein said cam groove formed on said cam ring comprises: a pluralityof first cam grooves, formed on an inner peripheral surface of said camring, for moving one of said two lens groups in said optical axisdirection in a predetermined moving manner; and a plurality of secondcam grooves, formed on an outer peripheral surface of said cam ring, formoving the other of said two lens groups in said optical axis directionin a predetermined moving manner.
 11. The lens barrel according to claim1, wherein said lens barrel comprises a zoom lens barrel having a zoomlens optical system including said lens group, a focal length of saidzoom lens optical system varying by rotation of said cam ring.
 12. Thelens barrel according to claim 1, wherein said rotation-transmission armand said engaging recess comprise a plurality of rotation-transmissionarms and a corresponding plurality of engaging recesses, respectively;and wherein said plurality of rotation-transmission arms are engaged insaid corresponding plurality of engaging recesses from the rear end ofthe cam ring in the optical axis direction, respectively.
 13. A lensbarrel comprising: a rotational ring driven to rotate about an opticalaxis by a motor; a cam ring rotated about said optical axis by receivinga rotational motion of said rotational ring to move at least one lensgroup in the optical axis direction via at least one cam groove formedon said cam ring; and wherein said rotational ring includes a pluralityof rotation-transmission arms extending in said optical axis direction;wherein said cam ring comprises: a plurality of bottomed engagingrecesses which are formed on an outer peripheral surface of said camring, and in which said plurality of rotation-transmission arms areslidably inserted to be relatively movable in said optical axisdirection with respect to said plurality of engaging recesses,respectively; and an outer flange formed on an outer peripheral surfaceof said cam ring to form a plurality of slots which penetratetherethrough in said optical axis direction between said outer flangeand bottom radial surfaces of said plurality of engaging recesses sothat said plurality of rotation-transmission arms are inserted in saidplurality of engaging recesses through said plurality of slots,respectively.
 14. A lens barrel comprising: a cam ring which is rotatedabout an optical axis to move at least one lens group in the opticalaxis direction via at least one cam groove formed on said cam ring; anda rotational ring which transfers a rotational motion to said cam ring;wherein said rotational ring includes at least one rotation-transmissionarm extending in said optical axis direction; wherein said cam ringcomprises: at least one engaging recess which is formed on an outerperipheral surface of said cam ring, and in which saidrotation-transmission arm is slidably inserted to be relatively movablein said optical axis direction; and an outer flange formed on an outerperipheral surface of said cam ring to bridge said engaging recess in acircumferential direction, so that said rotation-transmission arm isslidably inserted in said engaging recess so as to be positioned insideof said outer flange in a radial direction.
 15. The lens barrelaccording to claim 14, wherein said rotation transmission arm alsoextends in a circumferential direction of said rotational ring, andwherein the engaging recess is also formed in the circumferentialdirection in accordance with said rotation transmission arm, saidengaging recess extending in an area wherein said cam groove of said camring is not formed.